Composting Toilets ‐ their pros and cons and how they work.

It's a good idea to read this entire section before you start to build your own composting toilet. A basic composting toilet is not hard to build on your own but you need to get a good understanding of their operating principles.

The designs are cheap as they are made from a lot of recycled and easy to obtain materials. As such they may not be visually appealing to some members of the household! You probably wouldn't want to place it inside the main house.
Anyway, I don't think your local authorities would be impressed if you built one indoors. It's ironic, but on the one hand authorities often want water to be conserved, yet on the other hand, frown upon people building something that is cheap, natural and better for the environment than their own reticulated systems!

The design could also be useful for ranches, farms, wilderness cabins etc. In fact it could be installed in any situation where the distance from outbuildings and barns etc, to the main house or existing reticulated sewer system makes the expense of installing a new toilet system excessive. Use at your own risk and don't hold me accountable etc etc!

Design 1 was built mainly from existing or recycled / cheap materials for a total cost of about $150 to $200. It is designed for two to three adults to use when visiting the property every second or third weekend.
Design 2 is a twin-drum system, built for about $400 and is designed for more frequent use. It could probably support permanent full‐time use, although has not been tested for this.

Before I describe the two composting toilet systems I have built, some background information on composting toilets is needed. In short, if you don't take the time to get a good understanding of composting toilet principles, you can't expect them to work efficiently nor safely and you'll end up with (literally) a big mess!

Why have a composting toilet? There are many reasons to have one and probably just as many reasons not to. Maybe it would be easier if I discuss my own reasons.

I chose to build my own composting loo because‐
  • I own an empty section in a reasonably remote country village. The village is not large enough in terms of population to support a typical reticulated sewer system operated by local authority or commercial enterprise
  • I needed something that had very low running costs and could be left for long periods of time in‐between visits to the property
  • I wanted to use something other than the typically used anaerobic toilet system or septic tank
  • I couldn't afford to purchase a commercial composting toilet or the installation of a septic tank system
  • I have a "green" or "eco‐friendly" way of looking at things ‐ I feel guilty every time I flush a traditional toilet ‐ what a waste of water! The "flush and forget" mentality doesn't sit too well with me.
  • I like to build things and challenge myself!!

How do they work? Microbes! Simply do your usual "business", use toilet paper as you would normally, although it pays to use a brand of toilet paper that isn't bleached and laden with chemicals and fragrances. We'll talk about this later. Add a handful of special material when you're finished. There are a number of different materials that can be added. Garden soil is good material to use as a "starter" or from time‐to‐time as it contains "zillions" of microbes. Other materials to use include: peat, wood shavings and sawdust (non‐treated), fine bark chips, popped popcorn, shredded paper, dried grass clippings, and of course the toilet paper you add during normal use. These materials assist the composting process by allowing air to penetrate. I'll talk about this in more detail later.

What are they like to use? Probably the strangest thing I noticed when I first used mine, was, having done my "business" I'd stand up and automatically put my hand out to "flush", only to realize you don't flush!! It took a while to get used to that. Do they smell? Surprisingly, no! Certainly not in an unpleasant way. When you lift the lid you might smell a faint rich‐soil smell. This is totally normal and how they should be.

Maintenance The amount of maintenance needed depends on many factors;
  • the number of people using the system
  • how often the system is used
  • the design of the system
  • the air temperature / climate / season etc.
With 2 to 3 adults using it every second weekend, I have found there is virtually no maintenance for either of my designs. In summer, I sometimes add a little water if it looks like things are drying out a bit too quickly and every three to four months I use a special "paddle" to turn the compost over a little, just to help aerate things. No mess, no smell, maintenance is easy! I built my first system at the beginning of 2009 and at some stage I may have to remove the inner plastic lining, tie the top and leave it to sit in a warm position over summer to ensure any pathogens are truly "cooked" before burying the contents and starting again. Given that the system is used infrequently, I'm guessing I may never need to do this.

Advantages and Disadvantages of Composting Toilets? On the down side: you have to get familiar with the whole concept of how they work, you need to spend time planning, you have to spend time building it and sourcing materials. There are of course legal issues and local authority regulations and you need to decide if you want to do things properly and get approval, which could be a complicated process depending where you live. There are also possible health issues if you design and maintain it incorrectly and get it really wrong!

On the up side: save money ‐ Design 1 was built mainly from existing or recycled / cheap materials for a total cost of about $150 to $200. Design 2 was built for about $400 and is designed for more frequent use. I also feel like I am doing my bit for the environment. Building your own composting loo is a rewarding DIY project. You will be saving huge amounts of water and doing your bit for the environment.

Is it possible to build your own? If you're reasonably handy, YES! If changing a light‐bulb is as handy as you get, you might be better to get assistance or look at some of the commercial composting systems available. Electric toilets as used in boats and RV / campers are another option. Of course, you can go down the anaerobic route and purchase one of the many "self contained closed tank" chemical toilet systems, but depending on design you may be faced with having to empty the tank and then there's the possible harmful impact on the environment and cost of adding / using chemicals.

Composting Toilet Dos and Don'ts
    • add some suitable material each time you use it
    • decide whether you want to get your local authorities involved or keep it hush
    • as mentioned, understand how they work and I can't stress this enough. Take time to plan
    • do your research. Read all pages of this site before you start building it.  There are plenty of other sites about this topic out there too!
    • educate the people using it ‐ make sure they understand how to use it e.g. know not to use chemicals etc
    • monitor the compost carefully. As the system is an organic living thing, it is your responsibility to keep a close eye on the condition of the compost e.g. add more water if it's drying too quickly, reduce the airflow, add more heat etc

    • do not use chemicals! These will kill the microbes in the compost
    • do not rush into the building phase – plan it carefully first
    • do not put anything down the composting loo that won't decompose e.g. plastic wrappers from ladies' personal hygiene products

OK, with the basics over with, it is time to discuss some of these topics in greater depth.

Microbes Remember, these are the little invisible friends you need! There are trillions of different types of microbe on our planet. In fact, so many, no-one actually knows. Some live in water, some in dark, while others need light. In the case of a composting toilet, the aerobic soil microbes you get from the starter material, break down our faeces ‐ from now on I will simply call it "poo" Microbes need
  • fuel ‐ our poo and other added material we discussed earlier e.g. wood shavings
  • oxygen ‐ this is probably the main difference between a composting toilet and other types. Often a fan is used to draw air over the compost
  • heat ‐ the inner core of the compost will produce small amounts of heat on its own, but the addition of a little extra heat can speed-up composting performance. At the same time you don't want to "cook things". A fish tank heater is one option I will discuss in more depth.
  • moisture ‐ to keep things damp ‐ not too wet and not too dry. The amount of moisture affects composting efficiency. Too much moisture and you create "stodge". You'll effectively drown the microbes by reducing the amount of oxygen. Too little moisture and the microbes will not be able to breed and will die out.

Hope that doesn't sound complicated as it's simply about balance. Just make sure you understand the process and design the system to account for some of these things. Also, be prepared to adjust things manually to get that balance e.g. add some extra liquid if things are drying out too quickly.

Pathogens Pathogens harmful to us, evolved to live inside the human body. When outside the human body, such as when they are contained in a composting toilet, they don't live for long. Anyone using your composting loo who does happens to be infected with a pathogen, will "deposit" the pathogens into the heap. Providing the heap is contained, and I will discuss this as part of the design elsewhere, and, the people using it observe standard hand cleaning hygiene, pathogens won't survive and will quickly die out. If supplementary heat can also be added to your system (more about this later) so that the core reaches about 160 degrees F (about 70 degrees C) any pathogens are killed. However, this doesn't mean you must add extra heat. In most cases, containment and hand washing will suffice. Note too, if you live in a warmer endemic disease prone climate, the pathogen count may be higher than for those living in temperate climates.

Using the compost on a garden I think it's best to be cautious.If you are planning to re-use the compost in a garden, the generally accepted method would be to heat it (pasteurize it) to 160 degrees F (about 70 degrees C) to kill any pathogens, then bury it about 1 foot (30cm) deep away from tuber or root crops. This then creates the issue of heating the compost heap.
One of my designs deals with this by using an inner heavy-duty black plastic liner. This will be tied-off, removed and left in the sun to heat for several weeks, where it should easily reach the required temperature. Unless tested in a lab, you will never really know that it is 100% safe, so I suggest planning on the contain - heat - bury method. Keep it simple! My second design relies on supplying gentle heat, thermostatically controlled.

Urine Composting toilet systems usually try to remove urine from the main composting chamber to prevent excess moisture ‐ remember from above, you don't want to make "stodge". Urine can be removed in a number of ways. It can be separated before it gets to the compost chamber by use of an attachment or specially shaped porcelain bowl. This can be a bit of a fiddle for some users. Alternatively, urine can be allowed to enter into the compost chamber, drain through the compost and be re-directed via a urine drain to collection point for later removal, or, as you will see with my systems, piped to a separate drainage system.

Housing the Composting Toilet The easiest way to house your DIY composting toilet, is in a stand-alone garden shed, the type similar to the many kitset garden tool sheds available from garden centers and building supply stores.

a homemade wooden garden tool shed suitable for composting toilet   A homemade wooden garden tool shed can easily be converted to house a composting toilet.
  Purchase a kitset garden tool shed as an alternative to making your own. They usually come pre-made in flat panels with minimum assembly and are made from galvanized steel, aluminum or as pictured here, zinc coated.   The model pictured here doesn't come with a window, so an easy way around this is to make the shed, then remove one of the roof panels (usually just a few rivets need to be drilled-out), replacing it with corrugated plastic sheeting purchased from your building supply store. Just check the corrugated plastic is UV toughened and is of the same profile as the roof panel you remove. Make sure there are no obstacles likely to damage the roof nearby e.g. overhanging tree branches! Some of this plastic sheeting can be easily damaged - heavy hail stones can puncture some types. zinc coated kitset garden tool shed for composting toilet
kitset wooden garden shed to store a composting toilet   Another wooden garden shed which can be purchased in kitset form. Personally, I prefer the timber look as shown to the metal look of the previous design.
  Colored steel garden shed, available in kitset form. Once again, this model has no window, so you would need to modify it. a suitable garden shed to store a composting toilet